This invention relates to a tensioner which provides a fixed tension to a chain or a timing belt which drives a cam shaft of an engine in a car for tensioning it.
Generally, a tensioner is used for an engine as a chain tensioner or a belt tensioner. When the slackness of the chain or the belt occurs by the elongation or the abrasion thereof, the tensioner acts so as to push it in a fixed direction directly or indirectly and to maintain a fixed tension.
FIG. 19 presents a conventional example of such tensioner. As illustrated in FIG. 19, a male screw member 2 and a female scew member 3 are inserted within a casing 1 being threaded each other. The male screw member 2 is screwed with the female screw member 3 at the fore half portion of the male screw member 2, while at the latter half portion of the male screw portion 2 a coil spring 4 is inserted through the outside thereof. One end 4a of the coil spring 4 is inserted into a long groove 1a formed within the casing 4 and another end 4b is inserted into a slit of the male screw member 2, whereby the male screw member 2 is provided with a rotative force. On the other hand, the female screw member 3 penetrates through a bearing 5 secured to an opening end (left end) of the casing 1, the top end thereof (left end) being covered with a cap 6. A hole of the bearing 5 wherein the female screw member 3 penetrates therethrough, is formed to be a non-circular shape such as a small oval form or the like wherein opposite surfaces are deleted parallel and the outer form of the female screw member 3 is also formed to be a same one. In such a construction, the rotation of the female screw member 3 is restrained by the bearing 5 and the rotative force from the male screw member 2 changes to a pushing force to the female screw member 3, whereby the female screw member 3 advances directly in a drawing out direction from the casing 1 (left direction). Accordingly, the cap 6 at the top end of the female screw member 3 always urges the belt or the chain, whereby a constant tension is adapted to be maintained. In FIG. 8, the numeral 7 is a boot capable of elongation or shrinkage which covers the opening end of the casing 1, and the numeral 8 is a seal bolt scewed with a base end (right side) of the casing 1. These boot 7 and seal bolt 8 are provided in order to prevent the invasion of dusts from inside and outside of the engine into the casing 1 and to prevent the leakage of lubricant oil in casing 1 to the outward.
However, in such construction, it is necessary to be provided with the fore half portion wherein the male screw portion 2 is screwed with the female screw member 3 and the latter half portion wherein the coil spring is inserted through the outside thereof. In this case, a size of the male screw member determines a dimension of the device. As a result, a whole device becomes long in an axial direction. This direction is one which controls the tension of the chain or the belt. Accordingly, in view of installing the engine at a very narrow space, a short size is desirable and a long size is a fatal problem from the point of installation.
In order to intend shortening of such size, such an idea is proposed in which the male screw member, the female screw member, and the coil spring are combined with so as to be piled up in a diameter direction (Utility Model Laid-Open No. 62(1987)-115554. In this device, the female screw member screwed with the male screw member is rotated by the aid of the coil spring, whereby the male screw member is adapted to advance through the screwed portion. Since thus the male screw member is adapted to advance, a portion of the male member where performs a straight advancement being supported by a bearing is formed to be a non-circular sectional area agrees with the bearing, thereby constraining the rotation of the male screw member itself. This male screw member is possible to advance until a screw portion (circular sectional area) formed at the male screw member abuts against the bearing. However, in such a construction, the stroke of the advancing male screw member is stopped by the screw portion having a circular sectional area. Therefore, the stroke of the male screw member can not be secured sufficiently and the length for the tension controlling of the chain or the belt becomes smaller even if the shortening of the whole device is possible. By this, an adjustable range thereof is reduced and the practicability is also decreased.
In the conventional technic, when the device is long, the installation thereof to the engine or the like is difficult. On the other hand when the device is shortened, its stroke becomes short, whereby the range of the tension control is reduced.
The object of this invention is to provide a tensioner such as a chain, a belt or the like.
The object of this invention is to provide a chain, a belt or the like which satisfies the miniaturization of the device and the security of a sufficient range of the tension control.